How to make a hand held gadget that puts a fake read out on any blood pressure machine?

I talked to a electronics technician before, and he said it could be done. He said it could take some programming, but it could be done, and it would be very complicated. A custom hand held could do it, but not a PDA.

Is there anyone smart enough to build one?

Or perhaps a gadget that makes it not work right and the numbers don't come out?